Insulating material



Sept. 4, 1934. TQQHEY 5 AL 1,972,500

INSULATING MATERIAL Filed Sept. 26, 1951 INVENTO Edwardi Toohey.

ATTORNEY Patented Sept. 4, 1934 UNITED STATES PATENT OFFICE INSULATINGMATERIAL Application September 26, 1931, Serial No. 565,398

10 Claim.

This invention relates to insulating material and more particularly tothermal insulating material of minimized vapor breathing properties asindicated by minimized change in volume or length of a unit of thematerial with variation in the relative humidity of air in contacttherewith. The invention pertains especially to such improved materialcomprising felted fibres of asbestos, wool, or other insulating productsin the form of commercial articles, such as tubular pipe covering.

Woven or felted fabrics are widely used in thermal insulation. Thusasbestos and wool are much used in the form of felts, of which so-calledasbestos paper and wool felt are examples. Asbestos paper is widely usedin tubular sections for application around pipes that are to beinsulated. The paper of which these sections are constructed may be anyof several forms, of which those enclosing air cells are among the mostimportant. This type may be corrugated, or corrugated and then crossindented, as described in U. S. Patent 1,444,397 to Seigle, and may bealternated in pipe covering with backing sheets of plain asbestos papercemented by water glass solution. Because of the specific advantages ofthe invention as applied to the manufacture of these forms ofinsulation, the invention will be illustrated by particular referencethereto.

A process of making asbestos air cell insulation in sections of tubularform comprises the following steps:

Usual asbestos paper forming ingredients, such as a mixture of 87% byweight. of Canadian short fibre asbestos, 12.8% of starch, and .2% ofcaustic soda are mixed in a paper beater and formed into a felt on acylinder paper machine. The felt is removed and dried continuously. Aportion of the paper is then corrugated, as for example, as described inU. S. Patent 1,444,396 to Seigle. This corrugated material is thencemented firmly to a backing sheet of plain asbestos paper, by means ofa solution of water-glass. The resulting product may be dried and usedas composited corrugated and plain asbestos paper, in single sheets ormultiply blocks, or it may be wound spirally into tubular form, as bybeing wrapped around a mandrel to give a thickness of as many plies asdesired. For the latter use, the plain backing paper is suitably used inlength a few inches greater than that of the corrugated paper so that,after the wrapping operation is completed, there will project a free endof the plain paper which may be cemented to the underlying ply toprevent the tube from unrolling after being removed from the mandrel andto give a smooth outer surface. The section of cylindrical pipe coveringis then dried, out to length desired, suitably 36 inches, and sawed andscored longitudinally so that it may be opened like a clam shell. Theremay then be glued or cemented around the product a covering, such as oneof canvas with a lap section for closing the horizontal joint when thesection is later installed around a pipe that is to be insulated. Theassembled section of pipe covering is then thoroughly dried, as in atunnel drier at a temperature below 150 F.

When pipe covering made as above described or in a similar manner isallowed to remain in contact with the atmosphere and then placed in useon a warm pipe, it is found that the insulation undergoes a shrinkagewhich is evidenced by contraction in length with consequent exposure ofa certain part of the pipe which was originally covered. Thus, it is notunusual to find up' to one foot of pipe exposed by shrinkage of thecovering for each 100 feet of pipe originally covered.

Various theories have been advanced to explain the cause of thiscontraction, sometimes followed by subsequent expansion when thecovering is cold, contraction again when the covering is warm, etc. Ithas now been discovered that this expansion and contraction depends inpart at least upon the relative humidity of the air in contact with theinsulating pipe covering and particularly upon the property of thehygroscopic binder, of which starch is an example, of absorbing moistureto an extent varying with the temperature and/or the humidity of thesurrounding atmosphere. In fact we have found possible a substantialreduction and, in some cases, practically complete elimination of thisundesired change in length of the pipe covering, without greatlyincreasing the weight or thermal conductance of the insulator, byfabricating it from asbestos fabric substantially free from capillarityfor water in all parts of the fabric, made in such manner as to minimizethe vapor breathing properties, as for example, from asbestos fibrestreated with a water repellent agent, in limited proportion, so appliedas to decrease substantially the absorption of moisture from arelatively humid atmosphere but to allow penetration of liquid waterinto the asbestos paper formed from such fibres. It has been found alsothat asbestos paper made in the. usual process and thoroughly dried willabsorb several percent, in many cases as much as 5%, of moisture whenallowed to shrink either very much less or not at all when subsequentlyapplied and used on heated pipes, as, for example, on pipes carryinglow'pressure steam.

The fact that the felted fabric or paper made from the treated fibres ispermeable to water 1 makes possible the use of an aqueous adhesive,

such as a solution of sodium silicate (water glass) or casein glue, forfirmly cementing one unit to another, as in the case of cementing acorrugated sheet to a backing sheet of plain surface.

The individual fibres associated with the hygroscopic binder are sotreated as to be given a reduced or negative capillarity for water, witha consequent minimized tendency to absorb moisture from the atmosphere,without closing the pores between the fibres of the finished fabric orpaper. Our process gives a maximum vaporproofness without filling thepores of the fabric with an agent that may ooze out on warming or, underany circumstances, increases substantially the thermal conductance.

While the invention may be embodied in various forms, an embodiment thatis preferred at this time is illustrated in the drawing, which shows across sectional view of a section of tubular pipe covering installedaround a pipe.

The pipe 1 is of conventional type for conveying steam or other fluid.Disposed around this pipe is tubular sectional pipe .covering consistingprincipally of felted fibers of asbestos or the like and water-repellentmaterial intimately associated therewith, as will be described later.The felted asbestos fibers are in the form of a plurality of compositedsheets of paper, including plain paper 2 alternated and adhered firmlyto corrugated sheets 3 by means of adhesive (not shown). The composite,forming a tube of substantial thickness of wall, is cut throughlongitudinally, on one side, as indicated at 4 and partway through onthe opposite side as illustrated at 5, so that the tube may be openedfor insertion around the pipe. The outer sheet of plain paper may extendover the joint 4, in the form of the flap 6.

The following example of one method of practicing this invention isgiven for the purpose of illustration.

2000 pounds of asbestos paper stock fibre, suitably a mixture ofCanadian or similar short fibres, are mixed in a paper beater of usualdesign, the roll being elevated, with sufiicient water to give a mixturesuitable for felting into paper on a paper machine. There is then addeda rather concentrated hot aqueous solution of 50 lbs. of soluble soap,such as common laundry soap, with which is emulsified 50 lbs. of meltedparafiine wax. At about the same time there is added to the beater abinding agent adapted to absorb moisture, suitably a mixture of 500 lbs.of starch in hot water at approximately 190 F. .There is then added anaqueous solution containing 35 lbs. of zinc chloride. Finally there isadded an aqueous solution containing 45 lbs. of aluminum sulphate (papermakers alum). The temperature of the water originally added with theasbestos fibre should be such that the final mixture is tepid, as, forexample, at a temperature of approximately 120 F. After all of theingredients have been added the beater roll is lowered to such aposition as to give very gentle beating to the mixture and rotated forabout five minutes. The mixture is then transferred to the stock tankfrom which it is furnished to the paper making machine for forming intothe asbestos paper of minimized breathing properties. The paper isfinished in a. usual manner. A paper weighing five to eight pounds perhundred square feet has been made and used satisfactorily.

During the mixing in the beater, the wax,

starch and other ingredients become intimately associated with theasbestos fibres in such a manner that these ingredients are uniformlydistributed throughout the paper made from the mixture, as distinguishedfrom simply a surface coating. The fibres are made individuallywaterrepellent.

Also, certain chemical reactions occur during the mixing. For example,the zinc and aluminum salts form insoluble soaps of the metals. Thesesoaps are precipitated in contact with the fibres, in part within thefibres of asbestos, in such a manner as to produce a maximum effect uponthe capillarity of the fibres for moisture, with a minimum effect inclosing pores between the fibres in the finished product.

Particularly satisfactory pipe covering of the type sold under the tradename Asbestocel and consisting of corrugated and cross-indented sheetsbacked with plain sheets and made into tubular sections, have beenconstructed of paper made as above described, with the units of plainand corrugated paper cemented firmly together by water-glass or otheradhesive applied in aqueous solution. Such pipe covering, driedthoroughly at 240 F. and then exposed to air at a relative humidity of55% and a temperature of approximately 60 F., for a week, increases inweight by less than 2%, frequently less than /2 of 1%. After suchexposure, the pipe covering applied to a low pressure steam line showspractically no shrinkage during use, as for example, less than 0.2% inlength and, in many cases, less than 0.1%. These favorable results maybe due to the minimized vapor breathing properties, although theinvention is not limited by this or any other explanation of the mannerof operation. We make use of all of the effects produced by thetreatment described.

That the product is not waterproofed in the usual meaning of the term isindicated by the fact that asbestos paper or asbestos air cell pipecovering or other insulating product made from this special asbestospaper will absorb liquid water. Thus, it has been found that a sectionof "AsbestoceP pipe covering made in accordance with our invention andthen immersed in water will absorb 30 to 40% of its weight of water.

In another example of a method of practicing this invention. there wassubstituted a different water-repellent agent, namely, a compositioncontaining wax, for the mixture of soap, paraifin wax, zinc chloride andalum used in the first example given. The wax was of such a quality andwas so applied to the fibres as to minimize the vapor breathingproperties, as indicated by decreased absorption of moisture from ahumid atmosphere, without closing the pores between the fibres in thefinished fabric. Thus there has been added to the beater chargecomprising asbestos fibres and starch as above, an emulsion of 34% byweight of centrifuged petroleum wax, 6% of pure crude Montan wax, and60% of water. Of waxes, on the anhydrous basis, there are usedapproximately 2 to 10 pounds, suitably not more than 5 pounds, for eachhundred pounds of finished paper. The paper so made is finished inconventional manner, including maintenance at an elevated temperature,to produce drying and also to cause melting of the wax compositionpresent. In another modification of this invention, wool and otherfibres have been substituted for the asbestos and starch of the twoexamples above. Thus, a well disintegrated or beaten mixture of woolscrap, suitably with. approximately 20% of disintegrated wood pulp orold newspapers, has been treated with a water-repellent agent in theform of one of the mixtures described above. The resulting product wasthen formed into a felt and fabricated into commercial insulators, suchas sectional pipe covering of tubular form, in the usual manner.

In a modification of the invention particularly suitable for use inmaking inexpensive but very satisfactory pipe covering of minimum weightand also minimized vapor breathing properties, decreased capillarity forwater is imparted principally to the fibers at or near the surface ofasbestos paper, the paper is then corrugated or corrugated andcross-indented, composited with a plain surface backing sheet which hasbeen similarly treated to decrease the capillarity of the surfacefibers, and the composite is wound into tubular pipe covering.

For the treatment of asbestos paper to decrease the capillarity of thesurface fibers for water, the paper is suitably sprayed with, immersedin, or otherwise coated with a fluid adapted to produce awater-repellent surface.

In one example of this modification of the invention, asbestos paper ismade and dried in a usual manner and then is drawn through a bathcontaining water-repellent materials in such manner as to coat bothsides of the paper. The treated paper is then dried and fabricated intopipe covering in a conventional manner. For the water-repellentmaterials there has been used satisfactorily an emulsion comprising 34%by weight of centrifuged petroleum wax, 6% of pure crude Montan wax, and60% of water, diluted with additional water, as, for example, 4 to 20times as much additional water as there was used of the total originalemulsion to give 6 to 30 parts by weight of total water to one part ofwax'es. The asbestos paper may be drawn through this diluted emulsion ata rapid speed, such as 200 linear feet per minute.

Another water-repellent composition which may be used in this process ofsurface coating by immersion or spraying consists of 28 lbs. of aluminumstearate, dispersed in a solvent therefor, as, for example, in 8.5 gal.of warm turpentine, and then diluted by the slow addition of 105 gal. ofhigh test gasoline, the temperature of the gasoline during the blendingoperation being maintained near the boiling point.

Another composition which may be used for the spraying or immersionprocess is one containing 2 parts by weight of aluminum stearate, 2 tot:

parts turpentine and approximately 100 parts of 2 parts of casein, onepart of ammonia water, one

part of orthodichlorobenzol, and 66 parts of water,

the mixture being made into an emulsion by vigorous agitation.

For some purposes the process of intimately associating thewater-repellent material with the inner asbestos fibers may be combinedwith the surface-treating process. Thus asbestos fabric may be made froma beater furnish containing the usual asbestos paper making ingredientsplus water-repellent materials, the asbestos paper so made may then bedried, and the surface treated with one of the compositions describedabove for coating the fabric by spraying or immersion.

Starch as used in the above examples is a binding or sizing agent. Itmay be replaced by other materials, as, for example, a rosin size. Thecaustic soda specified in certain examples may be omitted if its effectis not desired. As used, caustic soda facilitates the swelling orgelatinizing of the starch.

It will be understood that many variations from the details given in theillustrative examples may be made without departing from the scope ofthe invention. Thus, variations in proportions of materials used may bemade and many different types of insulating products may be fabricatedfrom the fabrics of minimized vapor breathing properties.

By the term permeable as applied to a product of minimized vaporbreathing properties is meant penetrability by liquid water or aqueoussolutions of cements, as distinguished from waterproofness imparted, forexample, by a heavy poresealing impregnation with a bituminous material,such as asphalt.

What we claim is:

l. A thermal insulating article comprising lightweight, permeable,corrugated paper, including asbestos fibres, a binding agent adapted toabsorb moisture, and a water-repellent agent.

2. Sectional pipe covering for thermal insulation comprising sheets ofpaper including felted asbestos fibres, a hygroscopic binder therefor,and water-repellent material in amount not in excess of 10%. of theweight of the paper;

3. A permeable insulating material comprising a fabric including feltedasbestos fibres, a hygroscopic binder therefor, and a surface coatingadapted to decrease the capillarity of the surface of the fabric forwater.

4. A permeable insulating material comprising a sheet including feltedasbestos fibers and a hygroscopic binder therefor and a surface coatingcomprising a wax composition adapted to decrease the capillarity of thesurface of the sheet for water.

5. A permeable insulating material comprising a felted asbestos fabricand a surface coating comprising Montan wax and a petroleum wax andadapted to decrease the capillarity of the surface of the fabric forwater.

6. A permeable insulating fabric of minimized vapor breathing propertiescomprising fibrous material, a hygroscopic binder therefor, and awater-repellent material of the type of aluminum stearate substantiallyuniformly distributed throughout the said fibrous material.

7. A permeable insulating fabric of minimized vapor breathing propertiescomprising fibrous material, a hygroscopic binder therefor, and alimited proportion of a water-repellent material intimately associatedwith the fibers, to decrease substantially the absorption of moisturefrom a relatively humid atmosphere and to allow penetration of thefabric by liquid water.

8. A permeable asbestos fabric, suitable for use 10. Sectional pipecovering for thermal insulation'oomprising spirally wound corrugatedsheets of asbestos paper alternating with plain sheets of asbestospaper, said paper consisting of felted water-repellent fibres, ahygroscopic binder therefor, and approximately 2 parts by weight ofmaterial of negative caplllarity for water to 100 parts or finishedpaper.

rzbwann A. TOOHEY. EARLE R. WILLIAMS.

